Digital Rights Management (DRM) is a great concern for digital content owners, such as owners of songs, movies, electronic books, documents and other types of digital media. Content owners try to sell and/or distribute their content in such a way to prevent the illegal copying of their content. For example, content, such as songs, ringtones, video clips and even movies are widely sold or licensed and distributed electronically, such as over the Internet. To prevent illegal copying, content typically includes copy protection mechanisms that prevent users from making illegal copies and otherwise preventing unauthorized use of content.
The Open Mobile Alliance Group (OMA) has established specifications and protocols, e.g., OMA DRM v2, that enable content providers to grant permissions defining how their media objects can be consumed. The OMA DRM is independent of the media object formats and the given operating system or run-time environment. The media objects controlled by the OMA DRM can be a variety of media types, such as games, ring tones, photos, music clips, video clips, streaming media, etc.
According to the OMA DRM, a content provider sends a media object to a user, and the media object is encrypted with a corresponding content encryption key. Also, either the content provider acting as a rights issuer or a separate rights issuer sends a rights object (RO) that includes the content encryption key encrypted with the encryption key of the user's device. The RO also describes the permissions granted to the user for the media object. Then, the device decrypts to recover the content encryption key, and uses the content encryption key to access the media object. An agent running on the device allows the user to consume the media object according to the permissions granted in the RO.
The OMA DRM also allows a user to setup a domain so a media object can be shared among all the user's devices. For example, a user may purchase a song and download the song to the user's desktop. Then, the user desires to load the song on his portable media player. The user registers the portable media player as a member of the domain, so the song can be loaded and played on the portable media player.
The domain allows a user to share content among several devices. However, the domain in the OMA DRM is inefficient or unusable in certain situations. For example, if a user has a movie stored on a portable device and wants to play the movie at a friend's home, the user would have to make the friend's device a member of the domain. However, the content provider may not allow the friend to is become a member of the domain, because the friend is not a family member or because the device is not one of the user's devices. Furthermore, if the friend is made a member of the domain, when the move is done playing, the friend would have to be removed from the domain. According to the OMA DRM, when a device is removed from the domain, all the remaining devices in the domain should get a new domain key so the removed device cannot get access to new content. This is very inefficient.
Furthermore, the OMA DRM does not allow different members of a domain to have different permissions to media objects. This makes it difficult to restrict certain user permissions, such as restricting rights for media objects not suitable for children.